1. Field of the Invention
This invention relates to benzoyl alanines and to their use as corrosion inhibitors for aqueous systems.
2. Description of Related Art
Corrosion problems arise in numerous industrial processes in which aqueous media come into contact with metal surfaces, principally with surfaces of iron, copper, aluminium, zinc or their various alloys. Examples of processes of the type in question are cleaning processes using aqueous industrial cleaner solutions, cooling processes using aqueous coolant systems and also combined cooling and lubrication in the metal-working field.
Thus, German Application No. 11 49 843 describes semiamides of maleic acid or succinic acid as additives for fuel and lubricating oils. One disadvantage of these compounds, however, lies in the fact that, in most cases, they are not soluble in water so that homogeneous dispersion throughout the process liquid cannot be guaranteed.
U.S. Pat. No. 4,207,285 also describes semiamides of maleic acid as corrosion inhibitors for aqueous systems. In this case, the alkyl groups attached to the amide nitrogen are said to contain from 9 to 12 carbon atoms. In addition, the amido acids formed are neutralized with mono-, di- or trialkanolamines or mixtures thereof.
In addition, corrosion inhibitors which have been proposed for iron in alkaline media include alkenyl succinic acids (German Application No. 29 43 963), long-chain sulfonamidocarboxylic acids (German Application No. 12 98 670), acyl sarcosinates (Winnacker-Kuechler, Chemische Technologie, C. Hanser-Verlag, Munich (1960), page 199) and alkali metal benzoates. Hitherto, fatty amines or imidazolines have mostly been used for iron in mildy acidic media, but never with entirely satisfactory results.
Alkali metal silicates or alkali metal benzoates are mostly used as corrosion inhibitors for aluminium in alkaline media, although they, too, are often unsatisfactory. One particular disadvantage of these compounds lies in the fact that they are only effective in very high concentrations.
In addition to inadequate protection against corrosion, the use of corrosion inhibitors of the above type often leads to a number of difficulties in terms of practical application. Heavy foaming of the compounds in aqueous solutions, poor solubility in water and/or poor stability to water hardness or inadquate stability in storage seriously restrict the practical application of some of the compounds mentioned. At the same time, attention also has to be directed to the often excessive toxicity of the compounds and to their extremely poor biodegradability.